Medical devices include devices designed to be implanted into a patient. Some examples of these implantable medical devices (IMDs) include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), or devices that include a combination of these capabilities or others. The devices can be used to treat patients or subjects using electrical or other therapies, or to aid a physician or caregiver in patient diagnosis through monitoring of a patient condition. The devices can include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and can include one or more sensors to monitor one or more other internal patient parameters. Other examples of IMDs include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
In addition to IMDs, medical devices also include other ambulatory medical devices, such as wearable medical devices (WMDs), such as wearable cardioverter defibrillators (WCDs). WCDs can include monitors that can include surface electrodes. The surface electrodes can be arranged to provide one or both of monitoring surface electrocardiograms (ECGs) or delivering cardioversion or defibrillation shock therapy.
Some medical devices can include one or more sensors to monitor a physiologic status of a patient. For example, a device can be configured to measure a cardiac depolarization of the patient, a thoracic impedance, or a patient posture, among other things. Such measurements can provide useful information concerning the health of the patient, such as can be used to indicate a therapy.
Methods and devices to assess cardiac function using information about ventricular activity and a QRS interval can be found in Boute et al., U.S. Pat. No. 7,930,026, entitled “MONITORING QRS COMPLEX TO IDENTIFY LEFT VENTRICULAR DYSFUNCTION.”